Myositis
Abstract Number 1244 - Novel Expression and Conformation of Histidyl-tRNASynthetase (HRS) in the Lung: Implications for Targeting Of HRS in Myositis-Associated Interstitial Lung Disease
Authors: Stuart M. Levine, Antony Rosen, Frederic B. Askin, Rubin M. Tuder, Livia Casciola-Rosen. Johns Hopkins University, Baltimore, MD
PURPOSE: Most autoantigens in systemic autoimmunity are susceptible to proteolytic cleavage by granzyme B (GrB) [a tcytotoxic lymphocyte granule protease]; however , their antigenic targets remain unknown. Mechanisms underlying the association of specific autoantibodies with unique clinical phenotypes remains unclear. This group’s previous work has proposed that novel expression and/or conformation of autoantigens in tissue-specific microenvironments may play a role in generating these phenotype-specific immune responses. The striking association of antibodies to HRS (Jo-1) with a myositis/interstitial lung disease (ILD) overlap syndrome (seen in up to 70% of patients), focuses attention on the possible role of HRS expression (and conformation) in the lung in disease initiation and propagation.
METHODS: Normal human liver, placenta, muscle, and lung tissue extracts were examined by SDS-PAGE and analyzed by immunoblotting using rabbit polyclonal antibodies recognizing Jo-1.
RESULTS: Jo-1 was expressed at higher levels in lung than in muscle (1.2- 1.7-fold increase as determined by densitometry). When tissue extracts were cleaved with 100nM GrB prior to elecrophoresis and immunoblotting with an antibody preferentially recognizing the GrB-generated fragment of Jo-1, minimal amounts of Jo-1 fragment were observed in liver, placenta, and muscle. Large amounts of fragment in all lung tissues tested (N=8), however, was seen. Immunohistochemical analysis of normal lung tissues (N=3) probed with an anti-HRS polyclonal antibody revealed robust cytoplasmic HRS expression in the alveolar epithelium, with little staining of the larger airways and vasculature.
CONCLUSION: Jo-1 is observed at higher levels and in a more cleavable conformation in lung than in other normal tissues, with greatest expression in the alveolar epithelium. Given the strong association between Jo-1 autoimmunity and ILD, these data focus attention on Jo-1 expression and conformation in the lung microenvironment (and specifically the alveolar epithelium) as a factor in initiating and sustaining anti-Jo-1 autoimmunity in the ILD seen in combination with myositis in antisynthetase patients.
COMMENT: This study takes the novel approach at looking at Jo-1 expression in lung tissue without histopathologic changes of ILD, as it relates to expression in other normal human tissue, including muscle. The robust Jo-1 expression in lung tissue as it relates to other tissue (including muscle) suggests that the lung microenvironment may be the site of initiation and perhaps propagation of the autoimmune response in patients with antisynthetase related lung disease. It is known that patients that not all patients with Jo-1 antibodies have clinically apparent ILD. Future studies should address the question of whether patients with myositis-related muscle weakness in the absence of ILD actually have sub-clinical lung involvement.